The invention relates to loudspeakers and, more particularly, to loudspeakers comprising panel-form acoustic radiating elements.
U.S. Pat. No. 6,058,196 to Heron discloses a panel-form loudspeaker comprising a resonant multi-mode radiator element being a unitary sandwich panel formed of two skins of material with a spacing core of transverse cellular construction, wherein the panel is such as to have ratio of bending stiffness (B), in all orientations, to the cube power of panel mass per unit surface area (xcexc) of at least 10; a mounting means which supports the panel or attaches to it a supporting body, in a free undamped manner; and an electromechanical drive means coupled to the panel which serves to excite a multi-modal resonance in the radiator panel in response to an electrical input within a working frequency band for the loudspeaker.
U.S. Pat. No. 4,506,117 to Fresard discloses an electroacoustic transducer comprising an inertial mass adapted to be attached rigidly by its base plate to a panel to be vibrated.
U.S. Pat. No. 4,392,027 to Bock discloses an interior aircraft panel which functions as a loudspeaker diaphragm when excited by an electromagnetic driver coupled to the panel.
In parent application Ser. No. 09/011,831, a transducer of the type described herein is disclosed as part of a loudspeaker when coupled to a panel member of the type disclosed in parent application Ser. No. 08/707,012. Such a panel member functions as a distributed mode acoustic radiator, and has capability to sustain and propagate input vibrational energy by bending waves in an operative area extending transversely of thickness often but not necessarily to edges of the member; is configured with or without anisotropy of bending stiffness to have resonant mode vibration components distributed over the area beneficially for acoustic coupling with ambient air; and has predetermined preferential locations or sites within the area for transducer means, particularly operationally active or moving region(s) thereof effective in relation to acoustic vibrational activity in the area and signals, usually electrical, corresponding to acoustic content of such vibrational activity.
This invention is concerned with loudspeakers which use the same type of transducer, coupled to any member which is capable of sustaining and propagating input vibrational energy by bending waves, regardless of the nature of the distribution of that energy across the member.
Accordingly, the invention is a loudspeaker comprising a member having opposed faces and a capability to sustain and propagate input vibrational energy by bending waves in at least one operative area extending transversely of thickness, and a transducer mounted on the member for vibrating the member forming an acoustic radiator which provides an acoustic output. The transducer comprises a motor coil assembly having a coil rigidly fixed to a tubular member, and a magnet assembly, having opposed pole pieces, the periphery of one of the pole pieces being disposed within and adjacent to the motor coil assembly, and the periphery of the other pole piece being disposed outside of and adjacent to the motor coil assembly. The magnet assembly has a central attachment portion rigidly attached to the member to be vibrated. The motor coil assembly surrounds and is spaced from the central attachment portion of the magnet assembly, and has a surrounding attachment portion rigidly attached to one face of the member in spaced relation to the central attachment portion of the magnet assembly. The motor coil assembly and the magnet assembly move in opposite directions when a signal current is applied to the motor coil assembly, whereby the motor coil assembly and the magnet assembly apply a couple to the member through their respective spaced attachment portions to launch bending waves into the member.
In an alternative form the transducer for the loudspeaker may have complementary motor coil assemblies and magnet assemblies mounted on opposite faces of the member, with a fastener tying the centres of the magnet assemblies together or push/pull operation.